ANTIOXIDANT ACTIVITY OF TANNIN-RICH EXTRACT FROM WATER LETTUCE (Pistia stratiotes) LEAF

Oxidative stress is a condition in which the free-radical substance is higher than the potential antioxidant in the human body. Therefore, exogenous antioxidants are needed to resolve this problem. Water lettuce (Pistia stratiotes) is an aquatic floating plant that contains several bioactive compounds, including tannins and exhibits antioxidant activity. However, since organic solvent extraction results in a crude polyphenol extract, purification is needed to remove the undesirable compounds. This study was aimed at determining the total tannin content and antioxidant activity of water lettuce leaf extract before and after the purification process. The purification was done using a solid-phase extraction method, the total tannin contents were analysed using Folin-Ciocalteu’s method, and the antioxidant activity was analysed using 2,2-diphenyl-1-picrylhydrazyl. The results showed that the purification process successfully removed undesirable compounds and increased the total tannin content of the extract from 8.71 ± 1.50 mg TAE/g of the dry sample to 13.84 ± 0.28 mg TAE/g of the dry sample. The antioxidant activities also increased after the purification from IC50 135.14 ± 22.44 µg/mL to IC50 78.45 ± 5.42 µg/mL. According to these results, the tannin from water lettuce extract can be used as a source of natural antioxidants and formulated as an ingredient in food supplements.